1. Field
The disclosure relates to a method and an apparatus for transmitting a control channel, and a method and an apparatus for receiving a control channel.
2. Description of Related Art
In order to meet wireless data traffic demands, which have increased since the commercialization of 4G communication systems, efforts to develop improved 5G communication systems or pre-5G communication systems have been made. For this reason, 5G communication systems or pre-5G communication systems are called beyond-4G-network communication systems or post-LTE systems.
In order to achieve a high data transmission rate, implementation of the 5G communication system in a mmWave band (for example, a 60 GHz band) is being considered. To mitigate propagation path loss in the mmWave band and increase the propagation transmission distance, technologies such as beamforming, massive multiple-input multiple-output MIMO, Full-Dimensional MIMO (FD-MIMO), array antennas, analog beamforming, and large-scale antenna technologies are being discussed.
Further, in 5G communication systems, development for system network improvement is under way based on an evolved small cell, an advanced small cell, a cloud Radio Access Network (RAN), an ultra-dense network, Device-to-Device communication (D2D), a wireless backhaul, a moving network, cooperative communication, Coordinated Multi-Points (CoMP), and reception-end interference cancellation. In addition, the 5G system has developed Advanced Coding Modulation (ACM) schemes such as Hybrid frequency shift keying (FSK) and quadrature amplitude modulation (QAM) Modulation (FQAM) and Sliding Window Superposition Coding (SWSC), and advanced access technologies such as Filter Bank Multi Carrier (FBMC), Non-Orthogonal Multiple Access (NOMA), and Sparse Code Multiple Access (SCMA).
Meanwhile, the Internet has evolved from a human-oriented connection network, in which humans generate and consume information, to an Internet-of-Things (IoT) network in which distributed components such as objects exchange and process information. Internet-of-Everything (IoE) technology, in which big-data processing technology is combined with IoT technology through a connection with a cloud server or the like, has also emerged. In order to implement IoT, technical factors such as sensing techniques, wired/wireless communication, network infrastructure, service-interface technology, and security technology are considered, and research on technologies such as sensor networks, Machine-to-Machine (M2M) communication, Machine-Type Communication (MTC), and the like for connection between objects has recently been conducted. In an IoT environment, through collection and analysis of data generated in connected objects, an intelligent Internet Technology (IT) service may be provided in order to create new value in peoples' lives. The IoT may be applied to fields such as those of smart homes, smart buildings, smart cities, smart cars, connected cars, smart grids, health care, smart home appliances, or high-tech medical services through the convergence of related art Information Technology (IT) and various industries.
Accordingly, various attempts to apply 5G communication to the IoT network are being made. For example, technologies such as sensor networks, Machine-to-Machine (M2M), and Machine-Type Communication (MTC) are implemented by beamforming, MIMO, and array-antenna schemes. The application of a cloud RAN as big-data processing technology is an example of the convergence of 5G technology and IoT technology.
In a downlink, the role of a control channel is very important in transmitting data and maintaining connectivity. Current communication systems including an LTE system operate a downlink control channel named a Physical Downlink Control Channel (PDCCH). A Base Station (BS) transmits most information (for example, allocated resource blocks, an allocated Transmission Time Interval (TTI), a Modulation Coding Scheme (MCS), Hybrid Automatic Repeat and request (HARQ)-related information, rank, and precoding information) of data allocation information in the downlink and uplink through the PDCCH. User Equipment (UE) receives data through the downlink and/or transmits data through the uplink on the basis of the transmitted allocation information.
The PDCCH may play the same role in an mmWave band 5G system based on beamforming. However, there are two significant differences as compared to LTE, which is not a beamforming-based system. First, the PDCCH may be transmitted through a beam corresponding to a particular UE in the mmWave band 5G system. Second, the PDCCH may transmit not only data, but also a Beam State Information (BSI) request and a Beam Change Indication (BCI) in the mmWave band 5G system. At this time, the BSI serves to secure a beam reception state of the UE and the BCI serves to inform the UE of a beam change.
In 5G systems, beamforming is a scheme of achieving an antenna gain in order to compensate for high path loss in the mmWave band, and is capable of performing transmission and reception with a predetermined quality or higher only within a narrow coverage area in both horizontal and vertical directions, in comparison with coverage of a sector antenna BS of LTE. Accordingly, in order to serve the sector coverage of a low-frequency band such as that of LTE, the 5G BS has restrictions in that the BS should provide a service with appropriate beams between the BS and the UE by configuring beams in various directions and steering the beams in various directions in a short time. For the same reason, the UE should also operate various narrow beams having a large antenna gain. Due to such restrictions, there are also restrictions in that all signals including the PDCCH should be transmitted through a beam suitable for a particular UE in the mmWave band. Accordingly, managing an operation for determining beams suitable for transmission and reception between the BS and the UE and maintaining the same is required.
Since beams suitable for transmission and reception between the BS and the UE may vary depending on the communication state, the beams for transmission and reception between the BS and the UE may be changed. A change in the beams used by the BS and the UE may be determined by the BS on the basis of beam state information measured by the UE, and the BS may transmit the beam change to the UE. Alternatively, the UE may determine beams having the best performance and make a request for changing the beams to the BS. When the beam change is incorrectly performed, transmission/reception performance may deteriorate. Moreover, in this case, the beams may be changed to a direction in which communication is impossible, and thus communication becomes impossible for a predetermined time.